Muwatta Imam Malik (Riwayat Ibn al-Qasim)

It is narrated from Umm al-Mu'mineen Sayyida Aisha (may Allah be pleased with her) that the Messenger of Allah (peace and blessings be upon him) was with her when she (Aisha, may Allah be pleased with her) heard the voice of a man who was seeking permission to enter the house of Sayyida Hafsa (may Allah be pleased with her). Aisha (may Allah be pleased with her) said: I said, "O Messenger of Allah! This man is asking for permission (to enter)?" So the Messenger of Allah (peace and blessings be upon him) said: "I think he is such-and-such a man, Hafsa's foster-uncle." Then Aisha (may Allah be pleased with her) said: "O Messenger of Allah! If such-and-such a man, who was her foster-uncle, were alive, could he come to me (in my house)?" The Messenger of Allah (peace and blessings be upon him) said: "Yes, the relationships that are forbidden due to (real) lineage are also forbidden due to fosterage."